Preparation of non-homogeneous metal stock having regions of relatively low notch sensitivity



E. J. RIPLING PREPARATION OF NON-HOMOGENEOUS METAL STOCK Aug. 18, 1964 3,144,712

' HAVING REGIONS OF RELATIVELY LOW NOTCH SENSITIVITY 2 Sheets-Sheet 1 Filed April 1, 1959 62 64,114, Jkwat,

ATTORNEYS Aug. 18, 1964 E. J. RIPLING 3,144,712

PREPARATION OF NON-HOMOGENEOUS.METAL STOCK HAVING REGIONS 0F RELATIVELY LOW NOTCH SENSITIVITY Filed April 1, 1959 2 Sheets-Sheet 2 H6 /4 (50 L5/ I INVENTOR ATTORNEYS United States Patent 3,144,712 PREPARATION OF NGN-HOMOGENEOUS METAL STOCK HAVING REGIONS 0F RELATIVELY LOW NOTCI-I SENSITIVITY Edward J. Kipling, Flossmoor, Ill., assignor toContinental Can Company, Inc, New York, N.Y., a corporationof New York Filed Apr. 1, 1959, Ser. No. 803,403 8 Claims. (Cl. 29-528) This invention relates to thepreparation of a non-homogeneous metal stock having laminar regions and regions of relatively low notch sensitivity adjacent such laminar regions, and the material produced thereby.

It is known to prepare a metal billet having a channel extending therethrough, and to roll such a'billet to reduce its thickness and increase its length, wherewith the channel separates two surface laminations and prevents their being welded together during the rolling, e.g. by prefilling the channel with a resist material which is extended along the length of the billet proportionately during the rolling. The edges of the billet and strip produce an integral connection of the laminations at the edges of the channel. The material so produced has superimposed laminations which can be expanded or separated so that a tube is formed from the strip.

A characteristic of the expanded tube is the presence of diametrically opposite projecting external fins or ribs which usually are about twice as thick as each lamination layer itself, and are the residue of the aforesaid integral edge connections.

When it is desired to make such a tube with minimum projections, the projecting fins or ribs can be cut off or bent down against the outer surfaces of adjacent parts of the lamination layers. However, when the wall thickness is to made small, e.g. 0.005 to 0.010" for a tube of 2 to 4 inches diameter, it is desirable to make .the lamination layers of metal which is hard or at least hardened by the rolling operation; and in such cases the metal tends to crack along the residual reentrant angles and at the angles where the ribs are bent down. If it is sought to reduce the projections of the ribs by trimming along longitudinal lines of the strip which are closely adjacent the edges of the internal channel, and then to reduce the projections by radial rolling or beating, the hard metal also tends to split along the channel edges.

According to the present invention, the regions of the strip which embrace the edges of the channel and constitute the projecting fins, are made of a metal which is softer and less notch-sensitive, i.e. it tends less to crack from a sharp notch, than the metal of the lamination layers which :extend between such regions, .so that the greater thickness of the metal at the ribs produces a strength thereat equivalent to that of the harder metal of the lamination layers.

Illustrative practices of the invention are shown in the accompanying drawings, in which:

FIG. 1 is a perspective view of a section of an ingot having parts of soft metal of relatively low notch-sensitivity, other parts of a harder and more sensitive metal, and cores of resist or anti-weld material enclosed by said parts, portions being omitted show the relation of parts.

FIG. 2 is a corresponding view of a second procedure.

FIG. 3 is a perspective view of a composite core structure for a modified form of ingot;

FIG. 4 is a perspective view of a section of an ingot made with the core of FIG. 3;

FIG. 5 is az-perspective view of another form of comosite billet;

FIG. 6 .is .a perspective view of a strip produced by rolling the billets of FIGS. 1, 2 and 4;

FIG. 7 is a perspective view of a section of single-wide strip obtained by slitting the strip of FIG. 6 or rolling the billet of FIG. 5

3,144,712 Patented Aug. 18, 1964 FIG. 8 is a perspective view of the strip section of FIG. 7 after partial opening or expansion;

FIG. 9 is a perspective view of a cylindrical tube made by completing the opening of the strip section of FIG. 8, with the fins bent down;

FIG. 10 is a perspective view of a strip section as in FIG. 7, with the fins closely trimmed;

FIG. 11 is an end elevation of a part of the strip section of FIG. 10, after opening to cylindrical form;

FIG. 12 is an end elevation of the part of the opened tube of FIG. 11, after radial reduction of a projecting fin;

FIG. 13 is a perspective view, with parts broken away and at a greatly enlarged scale, to show the metal structure of the rolled strip of FIG. 7;

FIG. 14 is a sectional view at an enlarged scale, showing the regions of metal in the composite, with a superposed graph showing the increase of hardness, brittleness, and sensitivity with increase of alloying constituents.

Some dimensions have been exaggerated in the drawings, to emphasize the relationship of parts.

In FIG. 1 is illustrated a first form of a billet 10, which may be an ingot formed by casting in a fixed mold. This billet 10 is to produce a multi-wide strip upon rolling, and accordingly has four cores 11 arranged in a row or plane midway between the sides 12, 13 of the billet. Such cores 11 are prepared from an anti-weld or resist material such as finely powdered aluminum oxide, titanium dioxide, talc, silicon dioxide, or other refractory, transiently bonded by a frangible cement such as kaolin to provide a coherent body competent to withstand the pouring of the metal. Such cores are positioned within the mold walls illustrated in FIG. 1 by the dotted lines 14. The edges of the cores 11 are embraced by pre-shaped insert members 15 of metal which is less brittle, i.e. less notch-sensitive. than the metal which is to provide the major lamination layers of the strip produced. In FIG. 1, each end member 15 has a single groove 16 along its length for closely receiving an edge of the adjacent core 11, while the intermediate members 15 have two opposite grooves 16 for closely receiving the edges of the two adjacent cores 11; thus the members 15 can be seated against the mold walls and therewith serve to hold the cores 11 in position. The spaces 17 defined by the members 15, the cores 11 and the mold walls 14 are then filled with the metal which is to constitute the lamination layers and thereby provide the regions 15.

For examples, pure aluminum or a high-melting but soft alloy of aluminum can be employed for the insert members 15; while the spaces 17 are filled with and the regions 18 provided by an aluminum alloy of greater strength and lower melting point, but greater brittleness. The superheat of the molten metal is selected so that the poured metal will partly dissolve the members 15 superficially, while losing heat and therewith solidifying. This dissolution, with diffusion of the high melting metal from members 15 into the regions 18, produces intervening zones 19 united monolithically with the members 15 and regions 18 and providing transition there'between while connecting them together during the course of the subsequent rolling. In FIG. 1, the transition zones 19 are shown by surface hatching extending along the intervening regions.

Alternatively, as in FIG. 2, the cores 11 and insert members 20 of the harder but lower melting metal may be supported in the mold; and the spaces 21 filled with molten metal of the softer but higher melting type to provide the regions 22.. The insert members 20, in this practice are made narrower than the cores 11, so that the molten metal embraces the edges of the cores 11 and extends between adjacent cores as a connection 23, corresponding to the metal present between the pairs of grooves 16 in FIG. 1. As before, dissolution and formation of an inter-alloy occurs, with production of the transition zones 19. It will be noted that the billets of FIGS. 1 and 2 will be the same if like cores 11 are employed, like soft and low-brittle metal for the members and regions 22, and like harder and more brittle metal for regions 18 and member 20.

Such billets 10 may then be subjected to a hot-soaking, and a selected hot and cold rolling schedule by rolls acting on the opposite surfaces 12, 13 so that the thickness is reduced as shown in FIG. 6 with a proportionate increase in length but with little spreading in width. Therewith the two metals of greater and lesser hardness extend alike; and the cores 11 are similarly extended so that, in the final strip product, the thickness of the residues of the cores 11 bears substantially the same ratio to the thickness between the upper and lower faces in FIG. 6, as the cores 11 did to the thickness between the surfaces 12, 13. Each of the residues 25 of the core is a discontinuity at which the lamination layers 26 are separate and non-Welded over their adjacent faces, but joined at the ends by the integral face-to-face thicknesses 27 of the less brittle metal which spans the edges of the residues 25 and is monolithic with the lamination layers 26 by the residues of the transition zones 19, indicated by dash lines in FIG. 6.

Illustratively, the strips of FIGS. 6 and 7 may have a final total gage of 0.016 inch with lamination thickness of about 0.008 inch and width of 4.045 inches. The region or layer provided by the residue of the resist material is less than 0.001 inch. The softer spacer alloy extends to the edges of the laminations, terminating less than the lamination thickness therebeyond, e.g. 0.002 to 0.005 inch. The transition Zones 19 extend further along the lamination layers by 0.005 to 0.010 inch, depending on the schedule temperatures and times of heating operations. For this result, the original ingot can be 6 inches thick and 36 inches wide, having cores 11 which are 0.125 inch thick and 3.850 wide, separated by spacers 15 which are 0.140 inch thick, with milled channels 16 which are 0.010 inch deep and 0.125 inch wide to receive the cores; that is, the spacer thickness in the plane of the cores is 0.120 inch.

The strip of FIG. 6 is multi-wide, having four residue regions 25 corresponding to the illustrative four cores 11 in FIG. 1. This strip can then be split along its length, in the regions 27 of softer metal, to provide four narrower strips as shown in FIG. 7, each having a residue region 25 between two laminate layers 26 of harder metal, and with these layers connected by the edge portions 27 of softer metal. The transition or diffusion zones 19 are illustrated by the pairs of lines. This singlewide strip can then be expanded or opened out: wherewith the stronger and harder metal of each lamination 26 can bend into an are which is concave toward the interior of the tube without peripheral stretching, and the softer metal provided by the edge portions 27 in effect provides hinges with the internal surfaces becoming compound curves at each side of the reentrant angle A which establishes itself at the edges of the residue of the respective residue region 25, and with smooth external and internal surfaces at the junctions of the lamination arcs and the compound curves adjacent the reentrant angles and extending across the transition zones. Such strips can then be opened out and given a desired cross-sectional form. FIG. 8 shows a partial separation of the major lamination layers 26, with the edge portions 27 providing diametrically opposite, externally projecting fins. FIG. 9 shows the strip fully expanded into a cylindrical tube of circular section, and with the projecting fins 30 having been bent down against the outer surfaces of the major lamination portions 26. It will be noted that the bends for the fins are in the softer and less notchsensitive material which has provided the fins 30 and which as the portions 27 embraced the edges of the residue 25 of resist material.

In FIGS. 10-12, the fins 31 are shown as having been trimmed more closely to the edges of the residue along planes represented by the lines 32, with the trimmed-off scrap 33 shown by dotted lines in FIG. 10, so that these fins have a lesser radial projection, FIG. 11, beyond the general outer surface 34 when the tube is opened. Thereafter the fins 31, FIG. 11, can be beaten or rolled down as shown in FIG. 12, therewith slightly increasing the periphery of the tube and forming a land 35 illustratively somewhat thicker than the lamination portions 26. It will be noted that this radial reduction is being accomplished upon the softer and less notch-sensitive material, that is, the operation does not cause splitting along the reentrant angle A of the internal groove or crevice which is derived at an edge of the residue layer 25. Therewith the soft metal at its inner surface merges across the transition zones by smooth curvatures blending with the inner surfaces of the laminations; and the outer surface of the illustrated land conforms to the curved outer surfaces of the lamination but is spaced radially beyond the same. This radial reduction of the fins illustratively leaves the metal thereat with a greater thickness than in the portions of the wall provided by the lamination layers of the stronger metal. correspondingly this cold-working of the more ductile metal provided from the spacers acts to harden it, so that the strength of the tube can be made essentially uniform throughout the periphery. Such radial reduction is desirable when the tube is to be employed as a container (e.g. can) body.

When the strip is to be opened or expanded into a tube for use as a conduit, the fins can be left without trimming and radial reduction, for many purposes, and therewith the double thickness thereat affords strength at the connection regions between the major portions of the larninations.

It will be understood that the procedure described produces a composite in which the cold-rolled laminations of stronger and harder metal exhibit their qualities during the opening or expansion by being bent to the desired cylindrical or other shape, without significant peripheral stretching; while the opening occurs with the softer and more ductile spacer or connecting metal in condition to endure the stresses of opening out, and radial reduction when employed, Without the development of cracks.

The billet 35 of FIG. 5 has a core 36 of resist material, with portions 37, 37 of harder metal above and below it, and with edge portions 38, 38 of softer metal at its sides. Such a billet can be prepared by casting as above, or by providing the portions as bars of the same general shape but larger dimensions and subjecting the same to an extrusion operation with a central mandrel to provide a core space which is later filled with the resist material core 36: the abutting faces of the portions are welded together at the planes indicated by the lines 39 either during the casting or the extrusion. Upon rolling, a strip is produced as in FIG. 7.

An inner lining or cladding for the tubes produced may be included, e.g. the inner surface of the tube can be provided by the purer and thus more corrosion resistant metal, e.g. pure aluminum. A composite insert member as in FIG. 3 of such corrosion and notch resistant metal can be made with projecting outer ribs 40, the pockets or channels 41 for the cores of resist or anti-weld substance, and the webs 42 between and at the ends of such core spaces. The outer spaces 43 between the ribs 40 can then be filled, as by casting, with the harder metal which is to provide the major parts of the lamination layers, as shown by the bodies 44 in FIG. 4. The transition zones 19, where the connecting inter-alloy forms, is shown by the crossed hatching lines in FIG. 4. Upon rolling and splitting the multi-wide strip, a narrower strip is produced of which a part is shown in greatly enlarged scale in FIG. 13. The residue 25 of the resist material is surrounded by the soft metal 45, 46 which joins the harder metal 47 that provides the major thickness of the composite laminate layers 45, 47 above and below the residue layerZS. The transition zones 19 assure integrity of the structure. When this .strip is opened, as shown in FIGS. 7-12, the fins provided by the marginal portions 46 of soft metal permit the reduction of the distance of projection as shown in FIGS. 9 and 12.

The strips of FIGS. 6, 7 and 113 can be coiled and sold as such, for severing andopening by the purchaser. :In FIG. 14, a greatly enlarged section is shown, with the soft metal region 27 and the :hard metal region 26 shown by simple hatching, and the transition zone 19 shown by double hatching denoting the diffusion and formation of the inter-alloy. correspondingly the relative hardness is shown by the superposed graph line :50-51-52, in which the segment 50 shows a .low proportion of hardening component in the region 27 and the segment 52 shows a high proportion in the region 29,

softer and less notch-sensitive regions are provided thereby at points where the strip is to be later worked or bent. A heat treatment step may be employed for procuring the differential in brittleness: for example the major parts can be of the aluminum alloy known industrially as 6061, and the marginal and connecting parts of pure aluminum. After rolling, a heat treatment will effect strain release in the pure aluminum parts which are thus annealed and softened; While the heat treatable alloy parts respond by development of precipitation hardening components.

As an example of practice with aluminum alloys including components of heafitreatable type, the lamination body or casting metal 18 may .be of the aluminum alloys known commercially as 6061, 2024, 7075, while the spacers 15 can be selected from those known commercially as 1170, 1100 (2S), 3003 (3S), 3004, 5050, and

5052. After rolling to final gage (FIGS. 6 and 7), the strip can then be solution heat treated, at 800 to 970 degrees F.; and thereupon the spacer metal becomes completely annealed and is made soft and insensitive to notches, that is, not apt to fracture by propagation of a crack from the notch at the lamination edge during the opening and succeeding operations. The quenching which is a part of the solution treatment produces full age-hardening of the body metal, but has no effect upon the spacer metal, because the stated alloys harden solely during cold working. The radial reduction of the fin areas then provides such cold working.

Thus with a body or lamination metal of 2024 alumi-' num alloy, the hot-rolled thick strip can be heated to 650 degrees F. and slowly cooled: the CuAl and Mg Si compounds are precipitated in a matrix of softer material, which also carries insoluble compounds of Fe, Si and Mn. The subsequent cold-rolling causes Work hardening of the matrix. With the spacer metal of 1100 aluminum alloy, there are undissolved compounds of Fe and Si, with a matrix softer than the matrix of the body metal.

As another example of practice with aluminum alloys, with the components of types which respond to cold working by hardening, the lamination body metal may be of the aluminum alloys known commercially as 3003, 5052, and 5154 for developing the temper conditions known as H14, H16 and H18. The spacer metal can be of the alloys known commercially as 1170 and 1100. The temper values H14, H16 and H18 correspond to quarter hard, half hard and full hard tempers, developed by cold rolling reductions of approximately 40 percent, percent and percent. When a relatively purer aluminum alloy,

such as 1170 (99.7 percent aluminum) and 1100 (99.0

percent aluminum) as employed in the spacers, is cold rolled to the same degree, andthe aggregate then annealed at a low temperature such as 450 degrees R, such purer spacer metal is completely annealed while the body metal with higher alloying content is not thereby significantly softened. Such low temperature annealing acts to relieve stresses in aluminum alloys of higher alloying content such as the magnesium-containing alloys 5052 and 5154 so that they then exhibit the temper values known as H34, H36 and H38. Illustratively, the effects of such low temperature heating with a composite having 5052 alloy for the lamination metal and 1170 alloy for the spacers, can be stated as the cold-worked hardness values of H16 (hard) for both the laminations and spacers, which become H36 (hard) for the laminations and zero (soft) for the spacers upon such heat treatment. The H36 temper is not noticeably softer than H16, but the metal is more resistant to stress corrosion cracking.

Thus, with the body metal of 2024 aluminum alloy and the spacer metal of 1100 aluminum alloy, the hotrolled thick strip can be givena solution heat treatment of, for example, 30 minutes at 900 degrees F. and then quickly quenched in water. Therewith the matrix of the body or lamination metal is a solid solution with the CuAl and Mg Si compounds in dissolved form, i.e. in supersaturated solution at room and cold-rolling temperatures, so that the work hardening incidental to the cold rolling is increased by natural aging at room temperature or by an aging accelerated by heat treatment at 300-350 degrees F., whereupon a temperature value of T6 or higher-can be developed therein. The body matrix contains undissolved compounds of Fe, Si and Mn during the solution heat treatment and thereafter. The spacer metal responds to the solution heat treatment by recrystallization of the aluminum, and its content-of insoluble compounds is unchanged, so that this metal is softer than the body metal both before and after cold rolling, and after the aging treatment when employed.

The behavior of illustrative aluminum alloys, in annealed and in work-hardened condition, is indicated by the following:

1 Percent drop in ductility in presence of a sharp notch.

Ductility is stated as the elongation of a 2 inch length.

Bend Radius is stated as that upon bending a sheet-0.016 inch thick to an angle of degrees.

It will be noted in Table I, that all of the alloys will take a 90 degree bend at zero fillet radius when in the annealed or soft state, but that a fillet radius for noncracked condition is present for each in the hard state, and that this bend radius increases with the strength of the alloy in such condition.

It is also pointed out that hard-tempered aluminum alloys lose ductility when a sharp notch is present. For examples, 2024 and 7075 alloys then show a 90 percent loss of ductility. Thus a bare 2024-T6 sheet is highly susceptible to breakage when surface scratches are present, whereas an aluminum-clad sheet of 2024-T6 alloy is virtually immune to localized fracture when the aluminum coating is scratched.

The invention can likewise be applied to other metals where notch sensitivity is present after the rolling. For another example, the lamination body metal can be a relatively strong tin bronze, silicon bronze, or aluminum bronze; and the spacer metal can be a high purity copper such as the metals known commercially as electrolytic tough pitch and oxygen-free high-conductivity copper. After cold-rolling, a low temperature annealing at about 400 to 500 degrees F. causes a complete softening of the copper without significant softening of the work-hardened bronze.

The thickness of the transition zones 19 depends upon the schedule of heating temperature and times, increasing as the temperatures and times are increased. Such schedules can include homogenizing, hot-rolling, and processannealing. The transition zones appear to develop by solid state diffusion from the stronger body alloy into the purer spacer metal. Ranges of 0.002 to 0.020 inch are illustrative. The original overlap of the softer metal where it embraces the edges of the resist material is correlated to the time and temperature of the heat treatments, so that the reentrant angle A formed upon opening or expansion, and the regions adjacent thereto which will provide the hinge effect, are of the softer metal.

The invention is not restricted to the illustrative embodiments, but may be practiced in many ways within the scope of the appended claims.

What is claimed is:

1. The method of producing a metal tube, which consists of forming a billet having a plurality of transversely spaced longitudinal passages therein, the roll-engaging surfaces of the billet extending essentially in planes and having alternating regions of a stronger and a softer metal across its width, the stronger metal being notch-sensitive and subject to splitting when a strip rolled from a hollow billet thereof is bent at a reentrant angle, the softer metal being less notch-sensitive and not subject to such splitting, said softer metal regions extending from one said surface of the billet to the other between adjacent longitudinal edge surfaces of said passages, the harder metal being located between each said passage and the adjacent said surfaces of the billet, reducing the thickness of the billet with weld-preventing material in said passages and therewith extending its area and correspondingly reducing the thickness of the weld-preventing material, whereby to form a connected body having laminations of the stronger metal separated by the residue of the weld-preventing material, said laminations being connected at the edges of the said residue by said softer metal, and opening out the laminations to form a tube.

2. The method of producing a metal tube, which consists of inserting transversely spaced longitudinally extending softer metal spacer means in a mold with a core of weld-preventing material between each two adjacent spacer means, casting a stronger metal between the spacer means and against the cores and thereby forming a billet having a plurality of transversely spaced longitudinal passages therein formed by the said cores, the roll-engag ing surfaces of the billet having alternating regions of a stronger and a softer metal across its width, the stronger metal being notch-sensitive and subject to splitting when a strip rolled from a hollow billet thereof is bent at a reentrant angle, the softer metal being less notch-sensitive and not subject to such splitting, said softer metal regions extending from one said surface of the billet to the other between adjacent longitudinal edge surfaces of said passages, the stronger metal being located between each said passage and the adjacent said surfaces of the billet, reducing the thickness of the billet with weld-preventing material in said passages and therewith extending its area and correspondingly reducing the thickness of the weld-preventing material, whereby to form a connected body having laminations of the stronger metal separated by the residue of the weld-preventing material, said laminations being connected at the edges of the said residue by said softer metal, and opening out the laminations to form a tube.

3. The method as in claim 2, in which the spacer means have longitudinal grooves therein for receiving and supporting a said core between each two adjacent spacer means.

4. The method as in claim 2, in which the spacer means are connected by portions of the softer metal, said connecting portions covering the respective core.

5. The method of producing a metal tube, which consists of preparing a mold-insert spacer member of a softer metal, said insert member having longitudinal ribs projecting from its surfaces and longitudinal internal passages containing weld-preventing material, casting a stronger metal between the ribs and against the surfaces of the spacer member thereby forming a billet having a plurality of transversely spaced longitudinal passages therein, the roll-engaging surfaces of the billet having alternating regions of a stronger and a softer metal across its width, the stronger metal being notch-sensitive and subject to splitting when a strip rolled from a hollow billet thereof is bent at a reentrant angle, the softer metal being less notch-sensitive and not subject to such splitting, said softer metal regions extending from one said surface of the billet to the other between adjacent longitudinal edge surfaces of said passages, the harder metal being located between each said passage and the adjacent said surfaces of the billet, reducing the thicknesss of the billet with weld-preventing material in said passages and therewith extending its area and correspondingly reducing the thickness of the mold-insert spacer member and the weld-preventing material, whereby to form a connected body having laminations of the stronger metal separated by the surfaces of the reduced spacer member and the residues of the weld-preventing material, said laminations being connected at the edges of the said residues by said softer metal, longitudinally splitting the body along said softer metal regions and between said stronger metal regions and opening out the laminations to form a tube.

6. The method of producing a metal tube, which consists of mounting spaced bars of a stronger metal within a mold which cores of weld-resisting material between them, said cores being spaced laterally apart, casting a softer metal into the spaces between the bars and cores and against the cores and thereby forming a billet having a plurality of transversely spaced longitudinal passages therein formed by the said cores, the roll-engaging surfaces of the billet having alternating regions of a stronger and a softer metal across its width, the stronger metal being notch-sensitive and subject to splitting when a strip rolled from a hollow billet thereof is bent at a reentrant angle, the softer metal being less notch-sensitive and not subject to such splitting, said softer metal regions extending from one said surface of the billet to the other between adjacent longitudinal edge surfaces of said passages, the harder metal being located between each said passage and the adjacent said surfaces of the billet, reducing the thicknes of the billet with weld-preventing material in said passages and therewith extending its area and correspondingly reducing the thickness of the weld-preventing material, whereby to form a connected body having laminations of the stronger metal separated by the residue of the weld-preventing material, said laminations being connected at the edges of the said residue by said softer metal, and opening out the laminations to form a tube.

7. The method of producing a metal tube, which consists of forming a billet having a plurality of transversely spaced longitudinal passages therein, said billet being of a stronger and notch-sensitive metal at parts thereof located between each such passage and the respectively adjacent roll-engaging surfaces of the billet, said surfaces extending essentially in planes from side to side of the billet, said billet being of a softer and less notch-sensitive metal at the portions of the billet between the said passages, said softer metal portions extending from one rollengaging surface to the other and forming the longitudinal edge surfaces and at least parts of the upper and lower surfaces of said passages, reducing the thickness of the billet with weld-preventing material in said passages and therewith extending its area and correspondingly reducing the thickness of the weld-preventing material, whereby to form a connected body having laminations of the stronger metal separated by the residue of the weld-preventing material, said laminations having connections at the edges of the said residue consisting of said softer metal, longitudinally splitting the body along said softer metal regions and between said stronger metal regions moving the laminations apart to form a tube Wherewith the metal of the said connections is more greatly stressed than the metal of the said laminations, and reshaping the metal of said connections whereby to reduce the projections thereof from the outer surface provided by said laminations.

8. The method of producing a metal tube, which consists of preparing a body of softer metal having a plurality of transversely spaced longitudinal passages therein and having external longitudinal ribs located at the regions of the spaces between the said passages, casting a stronger metal into bonding contact with the sides of said ribs and with the surfaces of the body between said ribs and thereby forming a billet having a plurality of transversely spaced longitudinal passages therein, the roll-engaging surfaces of the billet having alternating regions of a stronger and a softer metal across its width, the stronger metal being notch-sensitive and subject to splitting when a strip rolled from a hollow billet thereof is bent at a reentrant angle, the softer metal being less notch-sensitive and not subject to such splitting, said softer metal regions extending from one said surface of the billet to the other between adjacent longitudinal edge surfaces of said passages, the harder metal being located between each said passage and the adjacent said surfaces of the billet, reducing the thickness of the billet with weld-preventing material in said passages and therewith extending its area and correspondingly reducing the thickness of the weld-preventing material, whereby to form a connected body having laminations of the stronger metal separated by the residue of the weld-preventing material, said laminations being connected at the edges of the said residue by said softer metal, opening out the laminations to form a tube.

References Cited in the file of this patent UNITED STATES PATENTS 377,317 Marshall Ian. 31, 1888 2,361,318 Orr et a1. Oct. 24, 1944 2,380,107 Hobrock July 10, 1945 2,411,024 Bruun Nov. 12, 1946 2,690,002 Grenell Sept. 28, 1954 2,749,609 Francis et a1. June 12, 1956 2,828,533 Fromson Apr. 1, 1958 2,983,993 Johnson May 16, 1961 3,050,848 Wilkins Aug. 28, 1962 FOREIGN PATENTS 4,794 Great Britain Feb. 17, 1894 205,695 Australia Jan. 10, 1957 

1. THE METHOD OF PRODUCING A METAL TUBE, WHICH CONSISTS OF FORMING A BILLET HAVING A PLURALITY OF TRANSVERSELY SPACED LONGITUDINAL PASSAGES THEREIN, THE ROLL-ENGAGING SURFACES OF THE BILLET EXTENDING ESSENTIALLY IN PLANES AND HAVING ALTERNATING REGIONS OF A STRONGER AND A SOFTER METAL ACROSS ITS WIDTH, THE STRONGER METALBEING NOTCH-SENSITIVE AND SUBJECT TO SPLITTING WHEN A STIP ROLLED FROM A HOLLOW BILLET THEREOF IS BENT AT A REENTRANT ANGLE, THE SOFTER METAL BEING LESS NOTCH-SENSITIVE AND NOT SUBJECT TO SUCH SPLITTING, SAID SOFTER METAL REGIONS EXTENDIGN FROM ONE SAID SURFACE OF THE BILLET TO THE OTHER BETWEEN ADJACENT LONGITUDINAL EDGE SURFACES OF SAID PASSGAES, THE HARDER METAL BEING LOCATED BETWEEN EACH SAID PASSAGE AND TGHE ADJACENT SAID SURFACES FO THE BILLET, REDUCING THE THICKNESS FO THE BILLET WITH WELD-PREVENTING MATERIAL INSAID PASSAGES AND THEREWITH EXTENDING ITS AREA AND CORRESPONDINGLY REDUCING THE THICKNESS OF THE WELD-PREVENTING MATERIAL, WHEREBY TO FORM A CONNECTED BODY HAVING LAMINATIONS OF THE STRONGER METAL SEPARATED BY THE RESIDUE OF THE WELD-PREVENTING MATERIAL, SAID LAMINATIONS BEING CONNECTED AT THE EDGES OF THE SAID RESIDUE BY SAID SOFTER METAL, AND OPENIGN OUT THE LAMINATIONS TO FORM A TUBE. 